C1: Carbon Chemistry OCR GCSE in Chemistry B Gateway Science J264 Name.. Form. This booklet contains a summary of the information and concepts in the C1 module. You ll need this material for your year 10 exam, and you should also refer back to it when you re revising for year 11. Take good care of this booklet! NOTE: the syllabus changed in 2011 and the letters and numbers (C1a, C1b etc) changed. Be careful when looking at older books and resources; they may reflect the old syllabus. The information in this booklet is correct for the course you re following.
C1a MAKING CRUDE OIL USEFUL Crude oil, coal and natural gas are all fossil fuels. Fossil fuels are finite which means they are either no longer being made (or are being made so slowly) that they re non-renewable because they are being used up faster than they are formed. The finite nature of crude oil causes a number of problems including; All readily extractable resources will be used up in the future. Finding alternatives to fossil fuels. Conflict between making petrochemicals and fuels. Crude oil is a mixture of many different hydrocarbons. It can be split into more useful products called fractions by fractional distillation. It works by: Heating the crude oil and passing it into a fractionating column which is cold at the top and hot at the bottom. Fractions containing mixtures of small range of hydrocarbons are obtained. Each fraction contains a number of substances of similar size, with similar boiling points. Smaller fractions with lower boiling points exit from the top end of the fractionating column and larger fractions with higher boiling points exit at the bottom end of the fractionating column. C1: Carbon Chemistry 2
The diagrams below show the hydrocarbon structures for propane and butane, which are both molecules found in crude oil. The lines between the atoms represent the covalent bonds that hold them together. These covalent bonds are very strong and are not easily broken. They are much stronger than the intermolecular forces between the hydrocarbon molecules and it is these intermolecular forces which are disrupted when the substance turns from a liquid into a gas (boils). Larger hydrocarbon chains have stronger intermolecular forces keeping the molecules together and therefore require more energy to boil; they have higher boiling points. Smaller hydrocarbon chains have weaker intermolecular forces and therefore require less energy to boil; they have lower boiling points. Cracking Propane Butane C 3 H 8 C 4 H 10 Oil companies have lots of larger, less useful hydrocarbons and a shortage of smaller, more useful hydrocarbons, which are in high demand, such as those used for petrol. They solve this problem by the use of a process called cracking that converts large alkane molecules into smaller alkane and alkene molecules. The smaller alkane molecules can be used as fuels; the alkenes can be used to make polymers (see C1d). The laboratory apparatus used for the cracking of liquid paraffin is shown below. It requires a catalyst and high temperatures. ceramic wool + paraffin clamp water heat aluminium oxide beads (catalyst) Bunsen valve Environmental problems Environmental problems caused by the use of crude oil include leakages (either from wells or during transportation). These leaks then lead to further problems such as damage to birds feathers causing death, and damage to wildlife caused by the use of detergents to clean up the oil slicks. C1: Carbon Chemistry 3
There are also a number of political issues to consider surrounding future supplies of crude oil to the UK from politically unstable countries. C1b USING CARBON FUELS There are seven things that you need to consider when choosing the best fuel. You can remember these using TEACUPS: T E A C U P S Toxicity how poisonous the fuel is. Energy value how much energy the fuel gives out. Availability how easy the fuel is to get hold of. Cost how expensive the fuel is. Usability how easy the fuel is to use. Pollution how much pollution is created by the fuel. Storage how easy is the fuel to store. The amount of fossil fuels currently being burnt is increasing due to increasing world population and growth of use in developing countries. Burning fuels The combustion of all fuels needs oxygen and releases useful heat energy. When hydrocarbons are burnt in lots of oxygen, carbon dioxide and water are produced. This is called complete combustion. The diagram below shows how you can test these products: The pump draws air through the apparatus as the hydrocarbon burns. The first test tube contains blue cobalt chloride paper; this turns pink in the presence of water, confirming its production. The second test tube contains limewater which turns cloudy as carbon dioxide gas is bubbled through it. The word and balanced symbol equations for the complete combustion of ethane are shown below; ethane + oxygen carbon dioxide + water 2C 2 H 6 + 7O 2 4CO 2 + 6H 2 O C1: Carbon Chemistry 4
Incomplete Combustion If fuel is burned without enough oxygen, incomplete combustion occurs. This forms the poisonous gas carbon monoxide and carbon (soot). The word equation for this reaction is shown below: ethane + oxygen carbon monoxide + carbon + water Complete combustion is better than incomplete combustion because: Less soot is produced, More heat is produced, Carbon monoxide is not produced. Bunsen flames When you heat something using a Bunsen burner, you are told to use a blue flame. This is because the blue flame is a result of complete combustion, whereas the yellow flame is due to incomplete combustion. The blue flame gives out more heat energy and is much cleaner because it doesn t produces soot like the yellow flame. C1c CLEAN AIR The air around us is a mixture of different gases in different proportions. It contains; 21% oxygen 78% nitrogen 0.035% carbon dioxide 0.9% argon 0.07% other gases The percentage of oxygen and carbon dioxide in the atmosphere remains constant because of the carbon cycle. This includes combustion and respiration which both use up oxygen and produce carbon dioxide. The word and symbol equations for respiration are: Glucose + oxygen carbon dioxide + water C 6 H 12 O 6 + 6O 2 6CO 2 + 6H 2 O Photosynthesis in green plants uses up carbon dioxide and produces oxygen. The word and symbol equations for photosynthesis are: Carbon dioxide + water glucose + oxygen 6CO 2 + 6H 2 O C 6 H 12 O 6 + 6O 2 C1: Carbon Chemistry 5
The balance of carbon dioxide and oxygen in the air can be disturbed by human influences such as: Deforestation Increasing energy consumption (which results in more fossil fuels being burned) Population increase The atmosphere developed into how it is today over millions of years. The key stages of its evolution are outlined below: Degassing of early volcanoes producing an atmosphere rich in water and carbon dioxide. Condensing of water vapour to form oceans. Dissolving of carbon dioxide in ocean waters. Relative increase of nitrogen due to its lack of reactivity. Development of plants that photosynthesize. Increase in oxygen levels due to photosynthesis. Common pollutants & sources: Carbon monoxide formed by the incomplete combustion of petrol or diesel in car engines. Oxides of nitrogen cause photochemical smog & acid rain formed in the internal combustion engine. Sulfur dioxide causes acid rain that kills plants and fish, and erodes stonework and some metals formed when sulfur impurities in fossil fuels burn. Catalytic converters are fitted to all new car exhausts to remove carbon monoxide and nitrogen monoxide. A catalytic convertor converts these harmful gases to nitrogen and carbon dioxide as shown in the symbol equation below: 2CO + 2NO N 2 + 2CO 2 C1d MAKING POLYMERS A hydrocarbon is a compound that is made up of hydrogen and carbon atoms only. Alkanes are one family of hydrocarbons, they contain only single covalent bonds between their carbon atoms. Compounds that contain only single C C bonds are called saturated and fit the general formula C n H 2n+2 propane C 3 H 8 C1: Carbon Chemistry 6
The covalent bond between the carbons in an alkane is made from two electrons, one from each of the carbon atoms. The carbon atoms share this pair of electrons. The hydrogen and carbon atoms also share an electron pair to form a covalent bond. Alkenes are another family of hydrocarbons, they are different from alkanes as they contain at least one double covalent bond between their carbon atoms. Hydrocarbons that contain double C=C bonds are called unsaturated. propene C 3 H 6 Testing for unsaturation You can test whether a hydrocarbon is saturated or unsaturated using bromine water, which is made by dissolving bromine (Br 2 ) in water. If ethane is bubbled through bromine water no reaction will occur and the mixture will remain a clear orange/yellow. However, unsaturated compounds will undergo an addition reaction, which causes the bromine water to become decolourised (turn colourless). This happens because one of the double bond breaks and the two reactants add together to form one single, colourless, dibromo compound. H H H H H C C H + Br Br Br C C H H Br colourless orange colourless Polymerisation Addition polymerisation involves joining monomers together by a series of addition reactions. Each monomer molecule is unsaturated, but the polymer is saturated. This reaction requires a high temperature or high pressure and a catalyst. The diagram below shows the polymerisation of ethene. Monomer Polymer You can see ethene on the left hand side and of the equation and poly(ethene) on the right. C1: Carbon Chemistry 7
C1e DESIGNER POLYMERS Polymers are used on a daily basis in a number of different roles. Examples of uses of polymers include polystyrene cups, polyester materials, plastic containers, PVC boots and many more. Structure of polymers The diagram below shows how polyethene is held together. You can see the strong covalent bonds holding the atoms together within chains. However the intermolecular forces between these polymer chains are weak and easily broken. This means that the plastics have low melting points and can be stretched easily as the polymer molecules can pass over each other. Some plastics have bonds between the polymer molecules (cross linking bridges). These plastics have high melting points and, because the molecules cannot slide over each other, they can t be stretched and are rigid. C1: Carbon Chemistry 8
Nylon and Gore-Tex Nylon is tough, lightweight and keeps liquid water and UV light out. However it doesn t let water vapour through it either, which means that sweat condenses inside the clothes and the wearer can become wet and clammy. Gore-Tex has all the properties of nylon but is also breathable. This is because it is made up of nylon laminated with a PTFE / polyurethane membrane, which contains tiny holes. These holes are too small for liquid water to pass through but are big enough for water vapour to pass through. The membrane has to be combined with nylon as it is too fragile on its own. Outer layer Sweat Wind/ rain Gore-Tex layer Protective layer Many polymers are non-biodegradable and so will not decay or decompose by bacterial action. This means that they have to be placed in landfill sites, burnt or recycled. This causes a number of environmental problems: Landfill sites are filling up and it is difficult to find new ones, When they are burnt toxic gases are produced Recycling is difficult as there are so many different types and mixed polymers are not very useful. In order to overcome these issues chemists are currently developing new types of polymers that are either biodegradable or dissolve. C1f COOKING AND FOOD ADDITIVES We know that cooking food is a chemical process because a new substance is formed, the process is irreversible and an energy change takes place. When we cook eggs or meat the protein molecules permanently change shape (called denaturing) which changes the texture of the food. C1: Carbon Chemistry 9
Potatoes contain a lot of carbohydrates. They contain cellulose, which forms the cell wall of all plants. Starch is trapped inside the potato cells. Uncooked starch is difficult to digest and cellulose can t be digested at all. However, cooking the potato causes the cell walls to rupture resulting in a loss of rigid structure and a softer texture. The starch grains are released, absorb the water, swell and spread out making them easier to digest. Food additives There are a number of different food additives with different functions; Antioxidants stop food from reacting with oxygen Food colours give an improved colour Flavour enhancers improve the flavour of the food Emulsifiers help oil and water to mix and not separate. Emulsifiers are molecules that have a water loving (hydrophilic) head that bonds to water molecules and an oil or fat loving (hydrophobic) end that bonds with oil or fat molecules. water oil droplet emulsifier molecule Baking powder Baking powder is used in cake mixtures in order to make the cake rise. It is able to do this as it contains sodium hydrogencarbonate, which breaks down (decomposes) in the baking process to produce carbon dioxide. This carbon dioxide causes the cake to rise and leaves lots of tiny little holes. C1: Carbon Chemistry 10
Sodium hydrogencarbonate sodium carbonate + water + carbon dioxide 2NaHCO 3 Na 2 CO 3 + H 2 O + CO 2 You can test to see if the gas released during a chemical reaction is carbon dioxide by bubbling the gas through colourless limewater (calcium hydroxide). If the limewater turns cloudy, then the gas is carbon dioxide. calcium hydroxide + carbon dioxide calcium carbonate + water Ca(OH) 2 + CO 2 CaCO 3 + H 2 O C1g SMELLS Cosmetics are either synthetic or natural depending upon their source. The organic compounds that give perfumes their smell are called esters. Perfumes Perfumes need to have certain physical properties including; Easily evaporates so that the perfume particles can easily reach the nose. Non-toxic so it does not poison you. Does not react with water (because otherwise it would react with perspiration). Does not irritate the skin. Insoluble in water so it isn t washed off too easily. How easily a liquid evaporates is called volatility. In order to evaporate particles need sufficient energy to overcome the attraction to other molecules in the liquid. Only weak attraction exists between the particles in the liquid perfume so it is easy to overcome this attraction. Esters Esters can also be used as solvents. A solution is a mixture of a solvent and a solute that does not separate out. Ethyl ethanoate is an ester that is a non-aqueous solvent, so it dissolves many substances that are not dissolved by water. For example nail varnish does not dissolve in water but does dissolve in ethyl ethanoate. This is because the attraction between water molecules is stronger than the attraction between water molecules and particles in nail varnish. It is also because the attraction between particles in nail varnish is stronger than the attraction between water molecules and particles in nail varnish. Esters are made by reacting an organic acid with an alcohol in the presence of an acid catalyst. An example is: acid catalyst ethanoic acid + ethanol ethyl ethanoate + water organic acid + alcohol ester + water C1: Carbon Chemistry 11
Testing cosmetics Cosmetics and perfumes need to be thoroughly tested before they can be sold in shops, so that they do not cause any harm or allergic reactions. The testing of cosmetics on animals is now banned in the EU because it doesn t necessarily show or predict the effect of the cosmetics on humans and therefore is unnecessarily cruel to animals. Animal testing however is not banned for pharmaceutical products. This is so medicines can be tested on animals and we can avoid doing unnecessary harm to humans but still move forward with pharmaceutical developments. In an exam, you need to be able to discuss and compare the advantages and disadvantages of animal testing. Make sure you give clear comparisons, e.g. animal testing allows you to predict the effect on humans, BUT it may harm the animals. C1h PAINTS AND PIGMENTS Paints contain a number of different ingredients all with specific purposes; Solvent thins the paint and makes it easier to spread. Binding medium sticks the pigment in the paint to the surface Pigment the substance that gives paint its colour. Paint is a mixture called a colloid. This is where the particles are mixed and dispersed with particles of a liquid but are not dissolved. The different component particles of the paint do not separate out because they are scattered throughout the mixture. The particles are also small enough so that they do not settle at the bottom. Most paints, such as emulsions, are applied as a thin layer that dries as the solvent evaporates. However oil paints use hydrocarbon oil as the solvent and consist of pigments spread throughout the oil. They often contain an extra solvent that dissolves the oil to form a solution. After the paint is applied, the solvent evaporates and the binding medium reacts with the oxygen in the air (oxidises) to form a paint film. Special paints Thermochromic paint, contains thermochromic pigments that change colour when heated or cooled. These can be used to coat a cup or kettle (to show when it is hot), or added to acrylic paints to give even more colour changes. For example yellow acrylic paint can be mixed with blue thermochromic paint to make green paint at room temperature but will then turn blue when heated. Phosphorescent pigments can glow in the dark. They are able to do this as they store energy and then release it as light over a period of several hours. They release this light energy whether it s light or dark outside (they don t know when it s dark) but usually the light is so faint you can only see it in the dark. These pigments are often used in watch faces or on road signs and are much safer than the dangerous radioactive sources that were used in the first half of the 20 th century. C1: Carbon Chemistry 12